1. Field of the Invention
The present invention relates to shore-side gantry cranes and more particularly to an improved articulated crane which in the stowed position with the gantry lifted to prevent interference with the movement of ships along the shore-side, the end of the gantry boom is disposed in an articulated position to lower its overall profile.
2. Description of the Prior Art
The present invention is an improvement upon a prior art articulating crane developed by the assignee of the prior art crane. That crane is described in U.S. Pat. No. 3,325,018 to Lawrence A. Wright for ARTICULATING CRANE, issued June 13, 1967. The disclosure of that patent defines the environment of the invention and its usefulness and it is therefore incorporated herein by reference.
Cranes used for unloading docked ships are usually mounted on tracks which run along the edge of the dock to permit the crane to be moved from ship to ship or to adjust to the ships variable docking positions. Cranes used for unloading cargo containers generally have the horizontal extension or boom called a gantry which projects over and across the deck of a ship. In order to position the boom across the ship or to remove it, the boom must be capable of movement in a vertical plate to avoid interfering with the rigging or superstructure of the ship. It therefore cannot be swung into position by rotating about a vertical axis. In order to effect the vertical movement of the horizontally extending boom, it generally must be rotated about its inboard end where it is hinged to the supporting structure.
In harbor areas there are often minimum height limitations for apparatus which extend out over the water when not in use to prevent such structures from interfering with passing or docking ships. On the other hand, there are sometimes maximum height limitations, if there are nearby airports, which must be observed.
With a large crane having a long boom, such limitations prevent the boom from being raised to a vertical position for storage in its fully extended position; even during movement to clear a ships rigging or superstructure. Thus, an arrangement cannot be used which causes the boom to swing horizontally or which permits it to swing straight up. Likewise it cannot be a structure which extends out over the water during storage, unless the projecting portion is above a minimum height, and, in order to be competitive cost-wise, the crane should not need to have any capability of rotating about a vertical axis. In essence, the boom must retract in a vertical plane while not exceeding a maximum height limitation or have over-the-water projecting portions depending below a minimum height limitation when retracted. This presents a difficult problem in providing an articulated crane which satisfies all of these conditions, but it will be observed that the present invention is a new and novel structure which meets and fulfills all of the requirements of the problem.